The invention relates to a method for forming a fine contact hole pattern of a semiconductor device.
As a manufacturing technology of semiconductor devices is developed and an application field of memory devices is enlarged, a technology of manufacturing a memory device of high capacity has been required with improved integration and un-degraded electric characteristics.
As a result, multilateral research has been made to improve photolithography processes, cell structures, and physical property limits of materials which form wires and insulating films.
It is difficult to form a contact hole pattern of less than 50 nm using a single ArF exposure process that has a numerical aperture (NA) of less than 1.0 even though an immersion lithography process is performed. In order to improve the resolution in the lithography process and enlarge a process margin, a resist flow process (RFP) or a method using a Resolution Enhancement Lithography Assisted by Chemical Shrink (RELACS) material (“0.1 μm Level Contact Hole Pattern Formation with KrF lithography by Resolution Enhancement Lithography Assisted by Chemical Shrink”, IEEE, pp. 12.5.1-12.5.4, 1998 Advanced Technology R&D Ctr., Mitsubishi Electric Corp.) has been developed.
The resist flow process that has been generally used includes patterning a resist and then flowing a photoresist material at high temperature to reduce a contact hole pattern size. However, in the case of the resist flow process, even when the same thermal energy is transmitted to the whole photoresist surface, the flow of photoresist is different in an upper portion, a middle portion and a lower portion of a contact hole. Also, since the amount of flowing photoresist is different depending on pattern density, it is difficult to obtain a fine pattern reduced with a uniform size.
For example, as shown in FIG. 1a, a lithography process is performed on a photoresist film 1 of an underlying layer to form a contact hole pattern 2. When a resist flow process is performed, as shown in FIG. 1b, a contact hole pattern 2-1 that has a smaller size than that of a desired contact hole is formed in a region having a low pattern density due to a large amount of flowing photoresist. Moreover, a contact hole pattern 2-2 is formed to be asymmetrical in left and right sides. In other words, it is difficult to obtain a contact hole pattern reduced with a uniform size over a wafer. As a result, it is impossible to obtain a stable process margin for a subsequent process, thereby degrading yield and reliability of the device.